Currently, in order to offer support to the knee joint, particularly during rehabilitation following traumas, lesions or surgical procedures, and/or during the practice of sports that are particularly onerous for joints, such as for example motocross, knee pads are used which are constituted by two frames that can be fixed respectively to the thigh and to the tibia and are mutually articulated by means of two appropriately provided hinges that during use are arranged proximate to the two sides of the knee.
The hinges guide the movement of the knee during the bending and extension of the leg, preventing such knee from performing abnormal movements that might harm it.
U.S. Pat. No. 4,886,054 is known, for example, which discloses a protective device for the knee, which is constituted by a first frame and a second frame, which are mutually articulated by means of two hinges constituted by a first flat base to the upper surface of which a second likewise flat base is fixed, its perimetric edge forming a cam arranged so as to cover at least partially the upper surface of the first base.
The hinges comprise a first arm and a second arm, which are pivoted to the outer surface of the second base, and a guiding block, which is fixed to the first base and has at least one guide that is provided with a first limit stop and with a second limit stop and is arranged so as to face the cam formed by the perimetric edge of the second base.
The hinges further comprise at least one stop lever, which has an elongated shape and is provided with a first end, which is pivoted to the first arm or to the second arm, and with a second end, which is slidingly associated within the guide formed in the guiding block; such stop lever is arranged proximate to the cam formed by the second base, so that during the rotation of the first or second arm to which such stop lever is connected, a portion thereof slides on the cam, pushing the second end of such stop lever within the guide.
The hinge further comprises a linkage, which connects the first arm and the second arm, so that the rotation of one of such arms causes the rotation of the other arm.
The rotation angle between the first arm and the second arm is limited by the abutment of the second end of the stop lever against the limit stops provided at the first and second ends of the guide.
This known type of solution, however, has a drawback: the first and second arms of the hinges in fact always move along two planes that are substantially parallel and constantly equidistant with respect to each other and therefore do not follow the actual motion of the knee, which is more complex in the various flexing conditions; accordingly, this can compromise both the support of the joint and the user comfort.
Further, these known types of hinge are structurally complex and therefore have a high cost.
Moreover, the stopping of the rotation of the hinges in both directions of rotation can be sudden, since it is achieved by means of the abutment of the second end of the stop lever arm against the limit stops provided in the guide, and this can compromise user comfort and safety.
WO03/065942 is also known which discloses a knee pad that comprises an upper frame and a lower frame, which are mutually connected by means of two hinges and are associated respectively with an upper sleeve and a lower sleeve, which can be arranged so as to wrap around the thigh and the calf of the user, and can be coupled thereto by way of two fastening elements provided with laces; such fastening elements are associated detachably with the respective frames by means of snap-acting buckles that allow, once the desired level of fastening has been set by means of the laces, to remove or put on the knee pad without losing the preset level of fastening.
Each hinge comprises an upper block and a lower block, which can be accommodated respectively in two complementarily shaped openings formed respectively in the upper frame and in the lower frame and can be locked in such openings by means of appropriately provided covers.
Two through openings are provided in the upper block and in the lower block and their lateral surface is shaped approximately like a spherical dome.
A front arm is arranged between one of the two openings of the upper block and one of the two openings of the lower block, and two hemispherical elements are associated with the ends of such front arm, are substantially shaped complementarily with respect to such openings and can be accommodated rotatably therein; a rear arm is arranged between the other two openings of the upper block and of the lower block, and two additional hemispherical elements are associated respectively with the ends of such rear arm, are substantially shaped complementarily with respect to such openings and can be accommodated rotatably in them.
The engagement between the hemispherical elements and the lateral surface of the respective openings allows the upper block and the lower block to perform mutual movements both parallel to the axis of the leg and in a radial direction with respect to such leg.
The hinges of such known type of knee pad further comprise a cable, in which a first end is fixed in an opening provided proximate to the end of the rear arm that is associated with the upper block and a second end is arranged in a channel formed in such upper block; the degree of protrusion of the cable from the channel can be adjusted by means of an appropriately provided adjustment screw.
The presence of the cable limits the rotation of the rear arm with respect to the upper block, and therefore of the upper frame with respect to the lower block, in the direction of extension of the leg; further, the cable has a slight elasticity, which creates a damping effect in the step for blocking the mutual rotation of the two frames in the direction of the extension of the leg, thus reducing the risks of possible traumas for the knee.
Even this known type of solution, however, has a drawback; it is in fact structurally complicated and requires a long time for its construction, and this entails a very high cost for it.
Further, the cable adapted to limit the mutual rotation of the upper frame and of the lower frame in the direction of the extension of the leg can be subject to frequent breakage, particularly due to the wear caused by its friction against the rigid components of the knee pad.
This known type of solution further has another drawback; due to the particular shape of the hinges, the upper frame and the lower frame can in fact be made to perform a translational motion with respect to each other, in the condition of maximum extension of the leg, in the direction defined by an axis that passes through the two hinges; this known type of knee pad, therefore, in the condition in which the leg is extended, is not able to protect the knee effectively against any stresses that tend to produce the lateral translational motion of the tibia with respect to the thigh.